The optically active epoxy compounds are widely used as an intermediate for various drugs including optically active benzopyran compounds effective for the treatment of hypertension, asthma and so on, and various methods for the synthesis of the optically active epoxy compounds have been widely examined. Among such synthesis methods, an asymmetric epoxidation is the most practical method, and since the discovery of asymmetric epoxidation using titanium tartrate as a catalyst (see T. Katsuki, K. B. Sharpless, J. Am. Chem. Soc. 1980, 102, 5974-5976), various synthesis methods using the asymmetric epoxidation have been developed (see E. N. Jacobsen, M. H. Wu, In “Comprehensive Asymmetric Catalysis” Ed. by Jacobsen, E. N.; Pfaltz, A.; Yamamoto, H. Springer (1999), Vol. II, Chap. 18.2, pp. 649-677. and T. Katsuki, In “Comprehensive Coordination Chemistry II” Ed. by McCleverty, J., Elsevier Science Ltd., Oxford, 2003, Vol. 9, Chapter 9.4, pp. 207-264).
However, many of these synthesis methods use an oxidant having a low atomic efficiency such as t-butyl hydroperoxide, hypochlorite, iodosobenzene or the like, so that it is strongly demanded to develop synthesis methods using an oxidant having a higher atomic efficiency and being environmentally benign. Among various oxidants, hydrogen peroxide is an environmentally benign oxidant because the atomic efficiency is high but also only water is produced after the transition of oxygen atom. For this end, asymmetric epoxidation using hydrogen peroxide as an oxidant has been studied vigorously, but there are very few cases where epoxidation could be attained with a high enantioselectivity (see L. Shu, Y. Shi, Tetrahedron, 2001, 57, 5213-5218. and S. Colonna, H. Molinari, S. Banfi, S. Julia, J. Masana, A. Alvalez, Tetrahedron, 1983, 39, 1635-1641). In many cases, there is a problem that the turnover number of the catalyst is insufficient.
On the other hand, the inventors have already discovered that (aRR Δ, aRR Δ)-di-μ-oxo Ti(salen) complex is exceptional as a catalyst for asymmetric sulfonation using urea-hydrogen peroxide adduct (UHP) as the oxidant (see B. Saito, T. Katsuki, Tetrahedron Lett., 2001, 42, 3873-3876). However, although the above (aRR Δ, aRR Δ)-di-μ-oxo Ti(salen) complex is good for oxidizing various sulfide compounds with a high enantioselectivity, it cannot promote the epoxidation of olefins.